Such pressure filtration apparatuses are used in filtration in which membrane filters are employed. Customarily pressure filtration is carried out at operational pressures ranging from about 5 to 15 bars. Such pressure filtration apparatuses may also be used for carrying out reverse osmosis.
Pressure filtration apparatuses of this type should have the maximum possible filtering surface available for the filtration and the smallest possible pressure space. Consequently, they are usually designed as flat, capsule-like, generally round pressure cells. The inflow is usually forced into the pressure space vertically from above and centrally over the filter. When an outlet is provided for the retained material or concentrate, the corresponding discharge channel is usually disposed peripherally.
In this fundamental design of customary flat pressure filtration apparatuses, it is particularly difficult in the case of concentrate reflux to distribute the inflow stream evenly or uniformly over the filter surface without the formation of dead space.
In one known pressure filtration apparatus of the type mentioned above, this problem is solved by means of a channel installed in the shape of a spiral and formed in the upper portion of the pressure filtration apparatus, the said channel being set on the membrane filter. The inflow is delivered in the center of the spiral and is then conducted over the filter surface, along the path defined by the side walls, up to the concentrate outlet on the periphery. The drawback of this apparatus lies in the fact that the inflow which is delivered under pressure impinges vertically directly upon the filter. There is great danger that the filter which frequently consists of only a single membrane might be damaged thereby. Another drawback in the known apparatus is that relative to the diameter of the free or open filter surface only a portion of this surface is available for the filtration. The filter area under the walls of the spiral and behind the outlet of the spiral channel is not available for the through-flow of the filtrate. Moreover, the filter surface that is actually available for the filtration is charged or loaded extremely heavily in an inhomogeneous manner. The inflow impinges on the filter at only a single point on a surface comprising only about one or two percent of the total available filter surface and clogs this area relatively quickly although the filter is still completely free at the discharge point. Therefore, the problem of uniform charging and utilization of the total filter surface has been solved only very incompletely by this so-called Thin-Channel-System.
In view of the existing state of technological development, it is the object of the present invention to create a flat pressure filtration apparatus of the type mentioned which will guarantee a mechanically sparing, uniform, and complete utilization of the total filter surface that is available in the pressure space.
In order to solve this problem a pressure filtration apparatus of the type mentioned at the outset is being proposed which, in accordance with the invention, exhibits the features described and claimed herein.